Buying a plot of land where a house previously burned down. What should be considered?

There are other options. For example, there are PUR panels for insulation. They insulate better than other materials at the same thickness. If the basement walls are properly insulated, wall heating is also possible. Don't bury your head in the sand. There are almost always options

Thanks, that motivates me! When the time comes, I will seek professional advice accordingly. I suppose that any architect-designed house can easily be adapted to the dimensions of the basement ceiling, but how is it with prefabricated house providers?

Depends on the flexibility of the [GU]. There are some who can even build a house on top of it for you

Also, the prefabricated houses in the classical sense can be built on without major problems. Are there plans of the old house? What definitely needs to be new is the electrical system in the basement. Then the heating—what was installed here before? That is more of a problem, or you have gas and can combine it with solar to comply with the energy saving regulations.

I think you actually have advantages because of the basement. When I think about how much disposing of the excavation costs nowadays and a living basement, plus the slope, and you get that more or less gifted with the property... Take it and be happy.

But here it would be more appropriate to have an architect with classical trades rather than a prefabricated house on top.

Great, yeah that's exactly how I think about it too. Yes, we have all the plans of the old house & there is actually still an old gas heating system in the basement, but we will get rid of it and probably also remove the old pipes. The electrical system will also be completely redone - I hope I can contribute some DIY work in both areas. If we don't need any gas at all, does it then have to be "disconnected"? So that the old gas meter can be returned? Or can you just turn off the valve somewhere and that's it?

Even traditional prefab houses can be built on top without major problems. Are there plans from the old house? What definitely needs to be renewed is the electricity in the basement.
Then heating, what was installed here before? That is rather a problem, or you have gas and can combine it with solar to comply with the energy saving ordinance.

I think you have more advantages because of the basement. When I consider what disposal of excavation costs nowadays and a living basement, plus the slope, and you basically get that more or less for free with the property... Take it and be happy.

But here, rather an architect with traditional trades should be involved than a prefab house.

Definitely no prefab house. We ourselves are in the process of building a basement that we bought. The plans did not match 100% with the >reality (but that was clear to us, as the previous owners messed up a lot) ergo, you have to expect some surprises. With a prefab company, we would have gone broke. Now we are building the thing ourselves with a friend, all the initial problems are solved and it is really running smoothly now.

With a prefabricated construction company, we would have become poor.

The (non)conformity of the plan and reality can be checked before building on an existing basement. I don't see where a timber frame panel general contractor would be inherently inferior to a stone-on-stone builder.